• Journal of Hydrogen and New Energy
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• v.33 no.4
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• pp.353-362
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• 2022

In this study, water diffusion in proton exchange membrane fuel cell at open circuit voltage (OCV) was analyzed through experiment. First, the reliability of the micro-sensor (SHT31) was verified. It was concluded the micro-sensor has an excellent reliability at 60℃ and 70℃. After the sensor reliability test, the temperature and relative humidity measurement in bipolar-plate was conducted at OCV. To analyze water distribution and water flux, the temperature and relative humidity was converted into dew point. To the end, it was found water concentration affects water diffusion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1503-1512
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• 2002

From the view of the environmental protection against the use of fossil fuels, a great of efforts have been exerted to find an alternative energy source. Hydrogen may become an alternative However the product species of the hydrogen flame is only $H_2O$, which emits only non-luminous radiation so the radiation from it is much smaller than that for a hydrocarbon flame. In this study, the authors designed and fabricated a laboratory scale test furnace to study thermal characteristics of hydrogen-air diffusion flame. In addition. the effects of addition of reacting as welt as non-reacting solid particles were experimentally investigated. Among the total heat flux to the wall, about 75 % was occupied by radiation while 25% by convection. When the aluminum oxide (Al$_2$O$_3$) particles were added, the radiative heat flux was reduced due to heat blockage effects. On the other hand, the total as well as the radiative heat flux was increased when the carbon particles were seeded, since the overall temperature increased. The effects of swirl and excess air ratio were also examined.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.526-534
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• 2004

A new second-moment closure model for turbulent heat fluxes is proposed on the basis of the elliptic equation. The new model satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. The predictions of turbulent heat transfer in a channel flow have been carried out with constant wall heat flux and constant wall temperature difference boundary conditions respectively. The velocity field variables are supplied from the DNS data and the differential equations only fur the mean temperature and the scalar flux are solved by the present calculations. The present model is tested by direct comparisons with the DNS to validate the performance of the model predictions. The prediction results show that the behavior of the turbulent heat fluxes in the whole region is well captured by the present model.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.129-139
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• 2002

From the view of the environmental protection against the use of fossil fuels, a great of efforts have been exerted to find an alternative energy source. Hydrogen may become an alternative. However the product species of the hydrogen flame is only $H_2O$, which emits only non-luminous radiation so the radiation from it is much smaller than that for a hydrocarbon flame. In this study, the authors designed and fabricated a laboratory scale test furnace to study thermal characteristics of hydrogen-air diffusion flame. In addition, the effects of addition of reacting as well as non-reacting solid particles were experimentally investigated. Among the total heat flux to the wall, about 75% was occupied by radiation while 25 % by convection. When the aluminum oxide ($Al_2O_3$) particles were added, the radiative heat flux was reduced due to heat blockage effects. On the other hand, the total as well as the radiative heat flux was increased when the carbon particles were seeded, since the overall temperature increased. The effects of swirl and excess air ratio were also examined.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.245-254
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• 2009

Efficiency of landfill liners system is usually evaluated based on leakage rate and mass flux. In this study, composite liner systems including the GCL(geosynthetic clay liner) composite liner, the Subtitle D liner, the Wisconsin NR500 liner, and the recently utilized double composite liner, which is a combination of the GCL composite liner and Subtitle D-type liner, have been examined. The leakage rate through circular and long defects in the geomembrane (GM) of the liner system was analyzed with the aids of analytical and numerical methods. For the mass flux criterion, contaminant transport through defects in the GM of landfill liners can be evaluated based on the calculated leakage rates. The diffusion rate of volatile organic compounds through intact landfill liners was evaluated by performing a one-dimensional numerical model. Cadmium and toluene were adoptted in the analyses as typical inorganic and organic substances, respectively, which will be chemical species encountered during landfill operation. The performance-based evaluation indicates that the double composite liner systems are superior to the other types of liner.

• Nuclear Engineering and Technology
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• v.24 no.3
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• pp.252-262
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• 1992

The intent of this study is to develop an efficient calculation method which can be used to analyze the heterogeneous time-dependent reactor problems. By using the nodal theory one can not only reduce the calculational efforts, but accurately determine the group dependent flux densities averaged over the entire homogeneous nodes. This method uses correction factors(called“discontinuity factors”) in a rigorous manner to obtain the relationship between the node-averaged flux and the surface-averaged fluxes and currents. The discontinuity factors are calculated from the node-averaged fluxes, diffusion coefficients, and the discontinuity factors of the previous time step. The test results for two benchmark problems demonstrate the accuracy and efficiency of the method developed for the transient application in which assembly-size nodes can be used.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.3
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• pp.117-122
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• 2020

In last few decades, although thermal and/or solutal buoyancy-driven recirculating flows in a closed ampoule have been intensively studies as a model problem, there exist interesting total molar flux of Hg₂Br₂ that have been unreported in the literature. It is concluded that the total molar flux of Hg₂Br₂(A) increases linearly and directly as the temperature difference regions in the range of 10℃ ≤ ΔT ≤ 50°, 3.5 × 10³ ≤ Gr_t ≤ 4.08 × 10³, 4.94 × 10⁴ ≤ Gr_s ≤ 6.87 × 10⁴. For the range of 10 Torr ≤ P_B ≤ 150 Torr, the total molar flux of Hg₂Br₂(A) decays second order exponentially as the partial pressure of component B (argon as an impurity), P_B increases. From the view point of energy transport, the fewer the partial pressure of component B (argon), P_B is, the more the energy transport is achieved.

• Membrane and Water Treatment
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• v.2 no.4
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• pp.239-250
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• 2011

A photovoltaic powered ultrafiltration and reverse osmosis system was tested with a number of natural groundwaters in Australia. The objective of this study was to compare system performance at six remote field locations by assessing the impact of water composition and fluctuating energy on inorganic contaminant removal using a BW30-4040 membrane. Solar irradiance directly affected pressure and flow. Groundwater characteristics (including TDS, salts, heavy metals, and pH), impacted other performance parameters such as retention, specific energy consumption and flux. During continual system operation, retention of ions such as $Ca^{2+}$ and $Mg^{2+}$ was high (> 95%) with each groundwater which can be attributed to steric exclusion. The retention of smaller ions such as $NO_3{^-}$ was affected by weather conditions and groundwater composition, as convection/diffusion dominate retention. When solar irradiance was insufficient or fluctuations too great for system operation, performance deteriorated and retention dropped significantly (< 30% at Ti Tree). Groundwater pH affected flux and retention of smaller ions ($NO_3{^-}$ and $F^-$) because charge repulsion increases with pH. The results highlight variations in system performance (ion retention, flux, specific energy consumption) with real solar irradiance, groundwater composition, and pH conditions.

• 연구논문집
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• s.24
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• pp.41-48
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• 1994

This experimental study deals with the extinguishiment characteristics of an oil pool flame using the water spray. The water through the six different atomizers is ejected over the freely burning pool flame in the quiescent surrounding air. Injection direction is vertical to the surface of oil in a small tank with a diameter of 100mm and a height of 10mm. In order to estimate quantitatively the extinction, the burning rate as well as the effective water flux are measured. The effective water flux is the amount of the water which reach the pool from the nozzle. The burning rate with the water spray increases until the injection pressure increases to reach some value, which gives the maximum burning rate, while the effective water flux without the flame decreases or does not change according to increasing of the injection pressure. This maximum burning rate is greater than 2.5 times of burning rate of the fire without the water spray. As a matter of the extinguishiment, it is found that the water drops of which size is too small can not extinguish the fire because too small drops does not reach the fuel surface.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2474-2482
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• 2023

The development of fast reactors with complex designs and operation status requires more accurate and effective simulation. The Monte-Carlo method can generate multi-group cross-sections in arbitrary geometry without approximation on resonances treatment and leads to good results in combination with diffusion codes. However, in previous studies, the coupling of Monte-Carlo generated multi-group cross-sections (MC-MGXS) and transport solvers has shown relatively large biases in fast reactor problems. In this paper, the main contribution to the biases is proved to be the neglect of the angle-dependence of the total cross-sections. The flux-moment homogenization technique (MHT) is proposed to take into account this dependence. In this method, the angular dependence is attributed to the transfer cross-sections, keeping an independent form for the total sections. For the MET-1000 benchmark, the multi-group transport simulation results with MC-MGXS generated with MHT are improved by 700 pcm and an additional 120 pcm with higher order scattering. The factors that cause the residual bias are discussed. The core power distribution bias is also significantly reduced when MHT is used. It proves that the MCMGXS with MHT can be applicable with transport solvers in fast reactor analysis.